Make a 6v 4ah Automatic Battery Charger Circuit without Using a Relay

The following 6 volt 4 AH battery charger circuit has been designed by me and posted here in response to the request from Mr. Raja, let's learn the whole conversation.

The Request

"Dear sir, please post a circuit to charge 6 volt 3.5 ah lead acid battery from 12 volt battery. The charger should automatically stop charging as the battery is fully charged. Please use transistor instead of relay to stop charging, and also tell me how to use 12 volt relay for the same circuit. Explain Which is safe and durable either relay or transistor to cut off charging. (At present i am charging my above said battery by simply using LM317 with 220 ohm and 1 kilo ohm resistors and a couple of capacitor) i'm awaiting your article, thank you".
The Design

The following circuit shows a simple automatic 6 volt 4 to 10 AH battery charger circuit using a 12 volt relay.

 The following circuit shows a simple automatic 6 volt 4 AH battery charger circuit without using a relay, rather directly through a transistor.

Both the above circuits will perform equally well, however the upper circuit can be altered to handle high currents even up to 100 and 200 AH just by modifying the IC and the relay. The lower circuit may be made to do this only up to a certain limit, may be up to 30 A or so.